In hydro-pneumatic vehicle suspensions the vehicle sprung mass can go above or below its normal static height range due to such circumstances as the loading or unloading of cargo, thermal expansion or contraction of the hydraulic fluid, or leakage of the hydraulic fluid. The present invention provides an auxiliary hydraulic system for passing hydraulic fluid into or out of the suspension actuator to control the vehicle height irrespective of such disturbing forces.
The auxiliary system includes a hydraulic pump, operated by normal suspension movement of the actuator, to pressurize an auxiliary accumulator. The auxiliary system also includes a directional valve for either venting liquid from the actuator (when the sprung mass is too high) or admitting pressurized accumulator liquid to the actuator (when the sprung mass is too low).
The system is particularly applicable to high speed tracked military vehicles having large numbers of closely spaced road wheels independently movable over rough terrain with minimal transmission of terrain roughness to the hull. Preferably a separate complete hydraulic system is provided for each roadwheel.